Increasing the volumetric sweep efficiency of secondary recovery petroleum production operations



United States Patent O INCREASING THE VOLUMETRIC SWEEP EFFI- CIENCY OF SECONDARY RECOVERY PETRO- LEUM PRODUCTION OPERATIONS Anthony F. Altamira, Houston, Tex., assignor to Texaco Inc., New York, N.Y., a corporation of Delaware Filed .lune 23, 1967, Ser. No. 648,354 Claims. (Cl. 166-9) ABSTRACT OF THE DISCLOSURE The volumetric sweep efliciency in secondary recovery is increased by locating the production Wells in the thinner zone of a reservoir and the injection wells in the thicker zone.

Field of the invention This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the overall production of hydrocarbons therefrom.

Description of the prior art Secondary recovery programs are now an essential part of the overall planning for hydrocarbon recovery from virtually every oil and gas-condensate reservoir in underground hydrocarbon-bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive the oil or gas toward production wells by the process frequently referred to as flooding Usually, this flooding is accomplished by drilling Wells in a geometric pattern, the most common being a tive-spot pattern.

As disclosed in the coassigned U.S. Patent No. 3,109,- 487, issued to Donald L. Hoyt on Nov. 5, 1963, the disclosure of which is incorporated herein by this reference thereto, an increasedamount of hydrocarbons is produced and recovered from an underground hydrocarbon-bearing formation by employing at least three wells penetrating such formation, which wells are in line, to produce hydrocarbons from the formation via two of these wells including the middle well. Further, as disclosed in the aforesaid patent, the hydrocarbons produced and recovered from the formation via the middle well are handled for further treatment, and extraneous uid, such as a water or gas, produced along with the hydrocarbons via the middle well is recovered and returned to the hydrocarbonbearing formation via the third of the aforementioned three wells.

In the copending, coassigned application for patent for Interface Advance `Control in Pattern Floods by Use of Control Wells, Ser. No. 517,052, there is disclosed how an increased amount of hydrocarbons is produced and recovered from an underground hydrocarbon-bearing formation by employing at least three wells penetrating such a formation, which wells can be in line, to produce hydrocarbons from the formation via two of these lwells including the middle Well as disclosed in the aforementioned coassigned U.S. Patent No. 3,109,487. This method of production may be defined as that of pinning the cusp.

In another copending, coassigned application for patent for Interface Advance Control in Pattern Floods by Retarding `Cusp Formation, Ser. No. 516,891, there is disclosed another aspect to increase the sweep efficiency which involves the retardation of the development of the cusp toward the production well. The method of achieving a more uniform advance is to control the flow gradients so that the interface is spread out, either by choosing a particular geometry of well positions or by adjusting the relative production rates so that the velocity of advance is not predominantly in one direction. It can be done also by shifting the gradients frequently, in both direction and magitnude, thus preventing any one section of an interface from advancing too far out of line. This method of production may be defined as that of spreading the cusp.

Summary of the invention An improved method to increase sweep efficiency in secondary recovery is disclosed herein and, in addition, incorporates the methods disclosed in the coassigned patent and the copendin-g, coassigned applications, and involves the location of production wells with respect to the thickness of the production zones of a reservoir. The disclosed method increases the volumetric sweep eiciency in secondary recovery operations by locating the production wells in the thinner zone of a reservoir and locating the injection wells in the thicker zone.

Accordingly, it is an overall object of this invention to provide an improved method for the production and recovery of hydrocarbons from underground hydrocarbon-bearing formations by an increase in the volumetric sweep efliciency thereof.

Another object of this invention is to include in this method for the recovery of hydrocarbons from an underground hydrocarbon-bearing formation, the recovery methods involving steps for pinning the cusp and spreading the cusp to increase recovery eiciency.

These and other objects and advantages of this invention will become apparent by reference to the following description when read in conjunction with the figures in the accompanying drawing, which schematically illustrates an embodiment of the practice of invention.

Brief description of the drawing FIG. 1 discloses four units of a conventional five-spot pattern of production wells;

FIGS. 2a and 2b disclose plan and elevation views of a potentiometric model of a quadrant of a conventional live-spot pattern, indicated by the dash lines in FIG. 1;

FIG. 3 is an elevation view showing a cross section of an underground dipping formation; and

FIG. 4 is another elevation showing in cross section a dome type of underground formation.

Description of the preferred embodiment Many factors dictate where production wells will be located in normal petroleum engineering operations. Usually, the location of the injection and production wells is not determined by the relative thickness of the reervoir. The novel feature of this disclosure is that one of the controlling factors foi the location of the injection or production wells will be the relative thicknesses of the reservoir. It would be the natural tendency, other things being'equal, to put the production wells in the thick section to obtain maximum productivity. It is postulated that around any injection well during a flooding operation, there is sweep-out of the formation. Accordingly, it would be to better advantage to Iget a greater volume of sweep-out in secondary recovery operations by locating the injection well where the formation has a greater thickness and to produce from the well penetrating a thinner part of the formation. The advantage to be realized by this is that substantially increased volumetric sweep of the reservoir is obtained for practically all mobility ratios which one might except to encounter.

- Referring to the drawings, FIG. 1 discloses four units of a conventional five-spot pattern wherein the corner Wells are shown as arrowed circles, to indicate an injection well, while the central well, shown as an enlarged dot, denotes a production well. As disclosed in the aforementioned copending, coassigned applications, the func- Patented Nov. 19, 1968 tions of these wells can change in accordance with the operation plan for exploitation of the reservoir in the underground formation.

FIGS. 2a and 2b disclose plan and elevation views of a quadrant section of a potentiometric model of a fivespot pattern, so reproduced because of the symmetry of the pattern, the elevation view being taken along line b-b of FIG. 2a. The production well is indicated at A as passing through the thinner zone h1 of the underground formation model and the injection well is indicated at B in the thicker Zone h2 of the formation model, with h1 being half as large as h2. The radius of the thicker zone h2 is indicated as r and is three-tenths the distance from A to B.

Three runs were made with mobility ratios =of 1, l and 0.1. The procedures were reversed and the injection Well was located in the thicker zone at B and the production well was located in the thinner zone at A. A tabulation of results follows:

I. Production Well in Thick Zone Injection Wellin Thinz0ne. i823 72-6' 57's II. Production Well in Thin Zone Injection Well in Thick Zone. 85 5 77' 8 69' 6 III. Uniform Thickness Throughout 81.7 71. 4 6l. 3

The above results show that the second procedure has a higher volumetric sweep-out than the other two procedures for all mobility ratios. This indicates that higher sweep volumetric efficiencies are to be achieved by locating the injection wells in the thicker zones of the reservoir and the production Wells at the relatively thinner zones. Most of the unswept part of the formation is in the vicinity of the production well where cusping will occur, while the reservoir in the vicinity of the injection well is completely swept out.

FIGS. 3 and 4 are cross-section views of different forms of underground formations. In FIG. 3, an injection Well is disclosed at B, which can correspond to either one or both of the wells along the right hand side of one of the five-spot patterns of FIG. l, A corresponds to the middle well of such a pattern, and A to either or both of the wells on the left hand side of this pattern, which wells now serve as production wells rather than as injection wells and penetrate in a formation zone of thickness h. As disclosed herein, production is initiated at A which well penetrates through the formation zone at thickness h, while injection occurs through well B penetrating the formation zone of thickness H. When the injection fluid reaches and is produced at production well A, then as disclosed in the above cited, coassigned patent to Hoyt, production is maintained at A while production at well (or wells) A' is initiated until breakthrough occurs. This is known as the pinning the cusp method. When it is decided that spreading the cusp is in the best interests of the exploitation of the field, then either of the corner wells on the left hand side of this five-spot pattern may -begin production, while production through the center well at A ceases, the production at the corner wells being continued until breakthrough of the fluid occurs thereat.

In FIG. 4, there is disclosed the manner in which a dome formation is exploited, where the apex of the dome is in the vicinity of the production Well A, penetrating the formation zone of thickness h, the injection wells, which are along the right hand side of one =of the fivespot patterns of FIG. l and are indicated at B, penetrate the formation zone of thickness H while the injection wells along the left hand side of such a five-spot pattern and indicated as B', penetrate through the formation zone of thickness of H. In each instance, H and H are greater than h, and may be either equal to each other or different. In FIG. 3, H is the greater dimension Iwhile h and h are respectively thinner.

Thus there has `been shown and described a method for increasing the volumetric sweep efficiency of secondary recovery fby a proper location of injection and production wells penetrating into a hydrocarbon-bearing formation in a production field, also utilizing methods for controlling the interface advance in pattern oods.

Obviously, other modifications and variations of the invention, as hereinbefore set forth, may ibe made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving an injection well and a production well which comprises introducing injection Huid into said formation via said injection well and producing hydrocarbons from said formation via said production well and maintaining the production of hydrocarbons therefrom until breakthrough of said injection fluid is observed thereat, said injection well being located to penetrate and extend through the entire interval a relatively thicker zone lof said hydrocarbon-bearing formation, and said production well being located to penetrate a Vrelatively thinner zone of said hydrocarbon-bearing formation.

2. In the method of producing hydrocarbons as defined in claim 1, said injection fluid comprising water.

3. In the method of producing hydrocarbons as defined in claim 1, wherein said injection iiuid is a gas.

4. In a method of producing hydrocarbons as disclosed in claim 1, the injection and production wells being part of a five-spot pattern.

5. In a method of producing hydrocarbons as disclosed in claim 4, said production well being at the center of said five-spot pattern and said injection well being at a corner thereof.

6. In a method lof producing hydrocarbons as defined in claim 1, initiating production of hydrocarbons at another production well located to penetrate a relatively thinner zone of said formation while maintaining production at the original production Well until breakthrough of said injection fluid is observed at the latter production well.

7. In the method of producing hydrocarbons as defined in claim 6, producing hydrocarbons from said formation via the original production well until largely extraneous uid is produced therefrom while maintaining production of hydrocarbons and extraneous uid at the second production well.

8. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving a centrally located injection well surrounded by production wells located on the diagonals of a quadrilateral with at least two of said production wells being substantially inline with said injection well and spaced thereby from a similar pair of said production wells positioned along the same diagonal, which comprises introducing injection fluid into said formation via said injection well, producing hydrocarbons from said formation via the production wells on said diagonals closer to said injection well, maintaining the production of hydrocarbons from the aforesaid production wells closer to said injection well when said injection fiuid begins to appear and is produced 'along with hydrocarbons via the closer production wells,

producing hydrocarbons from said formation via the production wells on said diagonals farther removed from said injection well, and maintaining the production of hydrocarbons from said production wells farther removed `from said injection well until breakthrough of said injection fluid is observed thereat, meanwhile producing hydrocarbons and said injection fluid from the aforesaid production Wells closer to said injection well, said injection Well being located to penetrate a relatively thicker zone of said hydrocarbon-bearing formation, and said production wells being located to penetrate the relatively thinner Zones of said hydrocarbon-bearing formation.

9. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving a centrally located injection well surrounded by production wells located at the vertices and along the sides of a quadrilateral which comprises introducing injection fluid into said formation via said injection well, intitiating and maintaining the production of hydrocarbons from the quadrilateral side production wells until breakthrough thereat of said injection fluid, and thereafter ceasing production of hydrocarbons thereat and initiating and maintaining producion of hydrocarbons from the production wells at the vertices of said quadrilateral until -breakthrough of said injection fluid thereat, said injection well being located to penetrate a relatively thicker zone of the quadrilateral side production Wells upon breakthrough of injection fluid thereat.

References Cited UNITED STATES PATENTS 1,872,906 8/1932 Doherty 166-9 X 1,885,807 11/1932 Doherty 166-9 X 2,048,731 7/1936 Doherty 166-9 3,319,712 5/1967 OBrien 166-9 X DAVID H. BROWN, Primary Examiner. 

